The shirt thing and the hotel room one earlier are annoying as it's hard to explain the answer. I think the trick is where the money is coming from.
The shirt cost $97 and there was $3 change, Mom and dad paid $98 for a $97 shirt and you have the other dollar (should be 49+49 they paid -1 that you have =97). Or maybe of the $100; $97 is in the shop and Mom, dad and yourself have $1 each.
As kids we had a silly thing to show we had 11 fingers; count down from 10 on one hand and say +5=11. Got me many a slap, sorry affectionate pat, on the head.